Was the corruption of Microsoft's "Tay" chatbot an example of catastrophic forgetting?
Looking at what happened, it was something similar. Though, the case differs in my eyes from one perspective: if it could only do a few comedy jokes, that probably is not a profound starting point to excel in Twitter.

Firstly, Twitter is about real life, not about comedy. Discussions are sometimes tough and you easily end up to Social Media Bubbles, where only a certain kind of speaking style and topics is cultivated. So, even humans get on the wrong track there; why not a newbie bot? And, with jokes you would probably catch something about language itself, but not about the topics. So, becoming a jerk instead of a nice comedian is a logical direction, where the bot even has to go, at least a little, to communicate on same level, and not alone. 

The comedian dataset compared to a Twitter dataset is also very small in a technical sense, so talking about a mini trend overkilling a megatrend in this case is probably not true, because of amounts of examples available. 

So, catastrophic things happened in learning, but not catastrophic learning with the definition of that term.